11 Jun
2002
11 Jun
'02
10:11 a.m.
On Tue, 11 Jun 2002, gfgs pedo wrote:
Book says, a construction that involved computing LSFR's over a field of 'odd charecteristics' is insecure. Does that mean a register with odd number of bits is insecure which would mean a tap sequence which uses an odd degree polynomial is insecure?
No, if you use bits for coefficients you are still in GF(2^n). What "odd characteristic" means is that you are in GF(p^m) with p odd (say 3 or 5 or 9). So you have a polynomial of the form x^3 + 4x^2 + 3 mod 5 is GF(5^4). 5 is the characteristic of the base field, and since it's odd it's a bad lfsr for crypto. Patience, persistence, truth, Dr. mike